1. Field of the Invention
The present invention relates to a gas laser oscillation device in which the axis of each discharge tube is aligned with the axis of a laser. In particular, the present invention relates to a gas laser oscillation device and an optical axis alignment adjustment method for the device, wherein the gas laser oscillation device comprises an optical resonance zone having two or more columns of discharge tubes which are connected at their bending portions by means of a bending unit, with each column made up of one or more discharge tubes which are connected in series, with a partial-reflection mirror at one end of the optical resonance zone and with a total-reflection mirror at the other end of the optical resonance zone.
2. Description of the Related Art
FIG. 8 illustrates the basic configuration of a gas laser oscillation device. Indicated at 1 in FIG. 8.is a discharge tube made of a dielectric material such as glass and the like. Indicated at 2 and 3 are metallic electrodes disposed in the discharge tube 1. A high tension power supply 4 is connected to the electrodes 2 and 3. The power supply 4 supplies, for example, a voltage of 30 kV across the electrodes 2 and 3. Indicated at 5 is a discharge space between the electrodes 2 and 3 in the discharge tube 1. A total-reflection mirror is designated 6, and a partial-reflection mirror is designated 7. An optical resonator is formed by the total-reflection mirror 6 disposed on one side of the discharge space 5, and by the partial-reflection mirror 7 disposed on the other side of the discharge space 5. A laser beam 8 is output via the partial-reflection mirror 7. An arrow 9 indicates the direction of gas flow. Laser gas circulates in the axial flow type laser device. A gas feeder pipe is designated 10. Heat exchangers 11 and 12 work to lower the laser gas temperature which rises as a result of discharge action in the discharge space 5 and the operation of a gas blower. The blower 13 is used to circulate the laser gas. The blower 13 causes a gas flow of about 100 m/s to take place in the discharge space 5.
The basic structure of the axial flow type gas laser oscillation device has been described above. Described below is how it operates.
The high tension power supply 4 supplies a high voltage between a pair of metallic electrodes 2 and 3, resulting in glow discharge in the discharge space 5. The laser gas that passes through the discharge space 5 receives energy from the discharge, and is thus excited. The excited laser gas is put into a state of resonance in the optical resonator formed by the total-reflection mirror 6 and the partial-reflection mirror 7. The resulting laser beam 8 is output through the partial-reflection mirror 7. The laser beam 8 is then used for welding, cutting, heat treatment, and other applications.
FIGS. 9A and 9B are a detailed view showing a conventional optical resonator portion of a gas laser oscillation device. Mounted on an optical resonator are an optical bench 14, clamps 16 and 17, discharge tubes 1, a bending unit 18, a partial-reflection mirror 7, and a total-reflection mirror 6. All of the clamps 16 are adjustable. Also mounted on the optical resonator is an adjuster 22 which aligns the optical axis by adjusting two total-reflection mirrors disposed on the bending unit 18. Specifically, a reference optical axis is first set up, and then, all of the clamps 16 and the total-reflection mirrors disposed on the bending unit are adjusted so that the optical axes of all optical elements agree with the reference optical axis. As described later with reference to FIG. 5, the clamps 16 are fitted into the optical bench 14 with a clearance fit. The clamps 16 are adjustable to within the clearance range which is allowed by clamp mounting screws (not shown) and their holes. The clamps 17 are integrally mounted on the discharge tube 1 as shown in FIG. 3; thus, the clamps 17 are installed along with the discharge tube 1 in order to fit into the clamps 16 after they are adjusted.
The following is a description of how the conventional optical axis alignment is adjusted. Indicated at 25 in FIG. 6 and at 26 in FIG. 11 are instruments which are used to visually inspect the position of the optical axis and which, made of translucent material, at their centers, have through holes 27a and 27b, respectively, of 0.5 to 1 mm diameter. Similar to the manner illustrated in FIG. 7, the instrument 25 may be installed on the clamp 24 on the mounting portion of the partial-reflection mirror 7. Both the accuracy of fit between the instrument 25 and the clamp 24 and the accuracy of fit between the clamp and the optical bench 14 are far better than an optical axis misalignment level normally considered as acceptable. As shown in FIG. 12, the instrument 26 is inserted into a hole (31 in FIG. 10) with the incidence side total-reflection mirror (28 in FIG. 10) of the bending unit 18 removed. As in the instrument 25, the instrument 26 is inserted into the hole 31 with a clearance fit far better than an optical axis misalignment level normally considered acceptable. Under the setup as mentioned above a helium-neon laser beam (hereinafter, simply referred to as laser beam), for example, is directed to the hole 27a at the center of the instrument 25 installed on the clamp 24. The helium-neon laser device is adjusted in positional setting so that the laser beam passes through the hole 27b at the center of the instrument 26. Indicated at 34 both in FIG. 12 and FIG. 13 is laser beam. Since the instruments 25 and 26 are made of translucent material, the laser beam creates a light spot on the areas of the instruments, if the laser beam fails to align with the holes. Such light spot allows the position of the beam axis to be visually located. After making sure that the laser beam passes through both the center hole 27a on the instrument 25 installed on the clamp 24 and the center hole 27b on the instrument 26, another instrument 25 is installed on one clamp 16 between the first instrument 25 and the instrument 26 as shown in FIG. 7. The clamp 16 is then adjusted and secured so that laser beam already set up passes through the center hole 27a of the instrument 16. This step is repeated until all clamps 16 are adjusted. After completing adjustment of all the clamps 16, the instrument 26 in FIG. 12 is removed, and is then refitted into the next hole (32 in FIG. 10) as shown in FIG. 13. The angle of the total-reflection mirror 28 is then adjusted with the adjusting screws 22 illustrated in FIG. 9 so that the laser beam passes through the center hole 27b on the instrument 26. Indicated at 21 is a total-reflection mirror unit having a total-reflection mirror 28. Next, the instrument 26 is removed from the hole 32, and the instrument 25 is installed on a clamp 23 (FIG. 9) at the end of the optical resonance zone after the total-reflection mirror 6 is removed. Both the accuracy of fit between the instrument 25 and the clamp 23 and the accuracy of fit between the clamp 23 and the optical bench are far better than an optical axis misalignment level normally considered as acceptable. After the total-reflection mirror 29 is installed on the bending unit 18 the angle of, the total-reflection mirror 29 is adjusted with an adjusting screw 22 so that laser beam passes through the center hole 27a on the instrument 25. Then, another instrument 25 is installed on one of clamps 16 arranged between the bending unit 18 and the clamp 23, and that clamp 16 is adjusted and secured so that laser beam passes through the center hole 27a on the instrument 25. Each of the clamps 16 should be adjusted as above. This completes the optical axis alignment adjustment in the entire optical resonance zone. If three or more discharge tubes are connected in series, similar additional adjustment are required between the bending unit and the total-reflection mirror at the end of the optical resonance zone.
In the above-mentioned prior art, the optical axis alignment procedure is complex and requires a high standard of adjusting skills, thereby consuming a great deal of time. The machining accuracies of the optical bench and other components have been improved in an attempt to shorten the time required for the optical axis alignment adjustment. Such an attempt has failed in achieving satisfactory results. Higher machining accuracy incurs higher machining costs. Furthermore, even high-accuracy components still result in cumulative errors thereby causing misalignment of the optical axis to occur, even to the extent that adjustment itself is impossible.